1. Field of the Invention
The instant invention relates to a method for manufacturing an isolating layer; in particular, to a method for manufacturing an isolating layer onto a crucible and a spraying device related thereto.
2. Description of Related Art
Nowadays, silicon ingots for the semiconductor or solar industry are manufactured using a necessary element, the crucible. The conventional crucible is made of quartz, but quartz will react with molten silicon to cause the molten silicon to adhere on an inner wall of the crucible, thus causing damage to the crucible. Accordingly, the inner wall of crucible needs to be coated with a silicon nitride layer to form an isolating layer, thereby extending the life of the crucible and ensuring the molten silicon within the crucible can be formed into silicon ingots with good quality. However, when forming an isolating layer on the crucible, thickness and uniformity of the isolating layer cannot be determined. Specifically, in a conventional method for manufacturing an isolating layer, the isolating layer formed on the inner wall of crucible cannot be manufactured to a desired thickness and uniformity, such that a crack easily occurs on the isolating layer resulting in reduction of the quality of the silicon ingots.
Moreover, in the polycrystalline-growth process of the solar industry, an isolating layer is prepared with high-purity for preventing molten silicon from directly contacting with a crucible, and the isolating layer is used as a release agent. When the isolating layer is not uniform enough or the isolating layer has a crack, the molten silicon may directly contact and adhere on the crucible. Specifically, the material of a polycrystalline crucible (SiO2) has a thermal expansion characteristic different from the silicon, so the silicon adhered on the crucible may increase a residual stress of the silicon ingots and may decrease yield of the silicon ingots in the cooling or processing processes. Furthermore, when the molten silicon directly contacts the crucible, impurity adhered on the inner wall of the crucible may diffuse into the molten silicon, thus reducing the quality of silicon ingots.
Therefore, how to provide an innovative method for manufacturing an isolating layer onto a crucible has become an important goal, in which the method needs to ensure quality and life of the crucible, good quality of the silicon ingots, and yield of the silicon ingots, thereby solving the conventional problems and reducing cost. Moreover, Taiwan patent No. 201033771 discloses a method for manufacturing an isolating layer, but this method needs to measure the inner wall of a crucible in a complicated way and needs to spray with high accuracy. However, the inner wall of each crucible is different and non-smooth, so the method disclosed in the above patent must gradually measure the inner walls of crucibles, which is obviously time-consuming. Accordingly, the method disclosed in the above patent needs to be improved.
To achieve the abovementioned improvement, the inventors strive via industrial experience and academic research to present the instant disclosure, which can provide additional improvement as mentioned above.